Abstract: The health system is ill-equipped to meet the needs of autistic adults. Our prior work has identified significant healthcare disparities experienced by autistic adults, including greater unmet healthcare needs, lower use of preventive services, and greater use of the Emergency Department (ED). A majority of primary care providers (PCPs) lack the skills needed to care for autistic adults, yet competing priorities make it unlikely they will attend trainings on autism. The heterogeneity of the autism spectrum may also make it challenging for PCPs to understand specific patients? needs. The Academic Autism Spectrum Partnership in Research and Education (AASPIRE), an academic-community partnership comprised of academics, autistic adults, healthcare providers, and supporters, has used a community based participatory research (CBPR) approach to develop and test an online healthcare toolkit aimed at improving primary care services for autistic adults. It was specifically designed as a low-intensity, sustainable intervention that can realistically be used in busy primary care practices that do not have a special focus on autism or other developmental disabilities. The toolkit includes the Autism Healthcare Accommodations Tool (AHAT)--an automated tool which allows patients and/or their supporters to create a personalized accommodations report for their PCP--and other targeted resources, worksheets, checklists, and information. Our pilot work has demonstrated that the AHAT has strong construct validity and test-retest stability, the toolkit is highly acceptable and accessible, and it has the potential to decrease barriers to care and increase patient-provider communication. Our long-term plan is to conduct a hybrid effectiveness-implementation trial, using a cluster randomized trial design, both to test the effectiveness of the AASPIRE Healthcare Toolkit in improving healthcare quality and utilization and to assess the utility of implementation strategies in diverse healthcare systems. The objective of this proposal is to use a CBPR approach to understand how to integrate the toolkit into these health systems, collect more robust efficacy data, and explore potential mechanisms of action. We will do so by conducting a 6-month pilot study with patients assigned to intervention and control clinics in three diverse health systems. We will meet our objectives by achieving the following specific aims: 1) to determine how to integrate use of the toolkit within diverse health systems; 2) to test the effect of the toolkit on short-term healthcare outcomes; 3) to use a mixed- methods approach to further explore the toolkit?s mechanisms of action; and 4) to refine our recruitment, retention, data collection, and system integration strategies in preparation for the larger cluster-randomized trial. Successful integration of this easily scalable and sustainable low-intensity intervention into primary care practices within diverse health systems will empower patients and providers to work together to improve health outcomes for a large, underserved, and understudied population with great barriers to care.